The rate of development from winter diapause to initial oviposition for Tetranychus urticae on strawberry, Fragaria x ananassa, in southwestern British Columbia, Canada, was linearly related to ...temperature above 9.4 ± 0.71°C. Initial oviposition (IO) in the field, defined as the day at which half of the leaflets with T. urticae also had T. urticae eggs (IO₀.₅), was determined for 21 populations between 1988 and 2006 by logistic curve fitting to sequential field samples. Prediction of IO₀.₅ required adjustment of air temperatures for the effects of cloud opacity on microclimate, otherwise predictions were 20-30 days late. A thermal summation start date of 27 November was determined by iteratively summing day-degrees (>9.4°C) from different start dates until IO₀.₅, for 10 calibration populations, and observing when the coefficient of variation for the mean thermal requirement was minimal. The thermal requirement for the 10 calibration populations was negatively correlated with accumulated cold-rest hours (<4.0°C). Model predictions of IO₀.₅ were not significantly different from the validation data. Predictions for 1954-2003 were positively correlated with the mean monthly Southern Oscillation Index (SOI) during September-December and negatively correlated with year (R ² = 0.36, P < 0.0001), indicating some potential for prediction of IO₀.₅ 2-3 months in advance. Estimated IO₀.₅ in 2003 was 12.8 days earlier than in the mid-1950s, and variation in IO₀.₅ related to the SOI was 25.2 days. These results may be generally applicable to other temperate arthropods that emerge at the same time as T. urticae, such as the aphids Chaetosiphon fragaefolii on strawberry, and Ericaphis fimbriata on blueberry.
Insects are selected for slow development (but relatively fast growth) in spring, but for fast development in summer. These contrasting selection pressure explain five puzzling effects of temperature ...on insects: growth and development rates increase almost linearly with temperature; genetic variability in development rate is reduced at high (27 degree C) temperatures; genetic variability in growth rate is reduced at low (15 degree C) temperatures; development is very slow at the time of emergence after diapause, regardless of the temperature threshold for emergence; and growth is slow at low temperatures, but development is even slower. Insects use temperature to indicate time-of-season. Different species are geared differently to rising temperatures. Insect predators and parasitoids become more effective at high temperatures; and insect population dynamics are not stable in the conventional sense.
Abstract
Aphids were sampled in commercial blueberry,
Vaccinium corymbosum
L. (Ericaceae), fields in southwestern British Columbia, Canada, from 2001 through 2003.
Ericaphis fimbriata
(Richards), the ...dominant aphid, overwintered as eggs on blueberry and emerged in late February and March during bud break. Apterous adult fundatrices were found during April. The fundatrices produced both alate and apterous virginoparae. There was a positive curvilinear relationship between production of alatae and aphid density on flower clusters, but not on leaf terminals. Peak densities in late June or early July varied from 300 to 9000 aphids per plant in different fields, suggesting that there may be considerable variation in
Blueberry scorch virus
transmission rates among fields infected with the virus. Production of alate virginoparae (percentage of all fourth-instar aphids with wing pads) declined from May through August. Sexual morphs were produced in late September and October. The efficacy of postbloom insecticide applications in June, by growers, was variable. Experimental trials showed that dormant oil is not effective in preventing aphid emergence. Aphids on blueberry should be controlled before bloom, before alatae are produced and large populations occur, but the efficacy of this approach in reducing virus transmission needs to be tested.
Résumé
Nous avons échantillonné des bleuetières commerciales à
Vaccinium corymbosum
L. (Ericaceae) dans le sud-ouest de la Colombie-Britannique de 2001 à la fin de 2003.
Ericaphis fimbriata
(Richards), le puceron dominant, passe l'hiver au stade d'oeuf sur les myrtilles et émerge à la fin de février et en mars lors de l'ouverture des bourgeons. Des fondatrices adultes aptères se retrouvent en avril. Les fondatrices produisent des virginipares tant ailées qu'aptères. Il existe une relation curvilinéaire positive entre la production d'ailées et la densité de pucerons sur les grappes de fleurs, mais non sur les feuilles terminales. Les densités maximales en fin de juin et au début de juillet varient de 300 à 9000 pucerons par plant dans les différents champs, ce qui indique qu'il peut exister une grande variation dans les taux de transmission du
virus de la brunissure nécrotique du bleuet
dans les champs infectés par le virus. La production de virginipares ailées (pourcentage de pucerons de quatrième stade avec des ptérothèques) décline de mai jusqu'à la fin d'août. Les formes sexuelles apparaissent à la fin de septembre et en octobre. L'efficacité des épandages d'insecticides par les producteurs en juin après la floraison est variable. Des essais expérimentaux montrent que l'huile de dormance n'empêche pas de façon efficace l'émergence des pucerons. Il faut faire la lutte aux pucerons sur les myrtilles avant la floraison, donc avant la production des ailées et la présence de fortes densités; cependant, l'efficacité de cette méthode pour réduire la transmission du virus reste à vérifier.
Traduit par la Rédaction
Abstract
Development rate and age-specific fecundity and survival of
Ericaphis fimbriata
(Richards) virginoparae were determined during the spring on young leaves of blueberry,
Vaccinium corymbosum
...L., as functions of temperature. The same traits were measured during the summer and the autumn on both young and mature leaves at 21.2 °C. The temperature threshold for development was 4.1 ± 0.5 °C (SE). For apterae, development time from birth to adult was 157.7 ± 5.9 day-degrees (dd). Proportional lengths of instars I–IV were 0.16, 0.14, 0.34, and 0.36, respectively. Adult life was 434.5 ± 17.5 dd and proportional lengths of the pre-reproductive, reproductive, and post-reproductive periods were 0.05, 0.74, and 0.21, respectively. Mean fecundity was 23.6 ± 1.0 nymphs per female. Mean survival was 602.9 ± 14.6 dd, and more than 80% of apterae survived the peak reproductive period. Alate fecundity was 16.5 ± 3.2 nymphs per female and alate survival was 460.9 ± 47.5 dd. Leaf type and season of measurement had significant effects on development time and fecundity: development time was 158.2 dd (+4.9 upper asymmetric SE) on young
V. corymbosum
‘Duke’ leaves in the spring but 312.4 dd (–16.9 lower asymmetric SE) on mature ‘Bluecrop’ leaves, the dominant leaf type, from a commercial field in the summer. Fecundity for the respective leaf types and seasons was 16.7 (–1.6) and 1.4 (+0.5) nymphs per female. From summer to autumn, development time increased on young ‘Duke’ and ‘Bluecrop’ leaves but decreased on mature ‘Bluecrop’ leaves; fecundity decreased on young ‘Duke’ and ‘Bluecrop’ leaves but remained at low levels on mature ‘Bluecrop’ leaves. A simulation model showed that seasonal changes in development time and fecundity were capable of reducing population growth rates to near zero depending on aphid distribution with respect to young and mature leaves. The results support a combined bottom-up and top-down view of aphid population regulation and suggest that control efforts should focus on the spring, when the population growth rate is maximal.
Résumé
Nous avons déterminé le taux de développement, la fécondité en fonction de l'âge et la survie en fonction de l'âge des femelles virginipares d'
Ericaphis fimbriata
(Richards) au printemps sur de jeunes feuilles de l'airelle
Vaccinium corymbosum
L. en regard de la température. Nous avons répété les mêmes mesures en été et en automne sur des feuilles jeunes et matures à 21,2 °C. Le seuil thermique du développement est de 4,1 ± 0,5 °C (ET). Chez les aptères, la durée du développement de la naissance à l'état adulte est de 157,7 ± 5,9 jours-degrés (jd). Les durées proportionnelles des stades I–IV sont respectivement de 0,16, 0,14, 0,34 et 0,36. La vie adulte dure 434,5 ± 17,5 jd et les durées proportionnelles des périodes pré-reproductive, reproductive et post-reproductive sont respectivement de 0,05, 0,74 et 0,21. La fécondité moyenne est de 23,6 ± 1,0 larves par femelle. La survie moyenne est de 602,9 ± 14,6 jd et plus de 80 % des individus survivent à la période de reproduction maximale. La fécondité des femelles ailées est de 16,5 ± 3,2 larves par femelle et leur survie est de 460,9 ± 47,5 jd. Le type de feuille et la saison dans laquelle se font les mesures ont des effets significatifs sur la durée du développement et la fécondité; la durée du développement est de 158,2 jd (+4,9, ET asymétrique supérieure) sur de jeunes feuilles « Duke » de
V. corymbosum
au printemps, mais de 312,4 jd (–16,9, ET asymétrique inférieure) sur des feuilles matures « Bluecrop », le type dominant de feuilles, dans une bleuetière commerciale en été. Les fécondités sur les deux types de feuilles et les deux saisons sont respectivement de 16,7 (–1,6) et de 1,4 (+0,5) larves par femelle. De l'été à l'automne, la durée du développement augmente sur les jeunes feuilles de types « Duke » et « Bluecrop », mais elle diminue sur les feuilles matures « Bluecrop »; la fécondité diminue sur les jeunes feuilles « Duke » et « Bluecrop », mais elle reste faible sur les feuilles matures « Bluecrop ». Une modèle de simulation montre que les changements saisonniers de durée du développement et de fécondité sont capables de réduire les taux de croissance de la population à presque rien, selon la répartition des pucerons entre les feuilles jeunes et matures. Ces résultats incitent à invoquer une combinaison de contrôles ascendants et de contrôles descendants pour expliquer la régulation de la population et indiquent que les efforts de contrôle devraient s'exercer au printemps au moment où le taux de croissance de la population est maximal.
Traduit par la Rédaction
The question “why sex?” is a longstanding fundamental puzzle in biology. Although there may be several answers, no satisfactory theory has emerged. We present an argument in favour of one function of ...sex, derived from a study of the population genetics and ecology of the cabbage butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae), on three continents between 1984 and 2009, and from previously published studies of other organisms. We provide evidence that responsiveness to directional selection (RDS), a measure related to “narrow-sense heritability”, can be dramatically reduced by truncation selection in a single generation and rapidly restored within a few generations. Viewing a population as a collection of sexual families, we show that rapid restoration of RDS after truncation selection is essential to maintain population variance. The only known mechanism that will rapidly restore RDS is sexual recombination. We therefore conclude that in P. rapae, sex restores the genetic variation that a population needs to match unpredictable environmental variation, despite selection tending to reduce that genetic variation.
Carabid populations were assessed in relation to type and level of nutrient input in a multi-year trial on tall fescue,
Festuca arundinacea. Thirteen species of carabids were recovered,
Pterostichus ...melanarius representing 81% of all catches. In 3
m wide strip plots populations of
P. melanarius increased with the rate of dairy slurry application, and the effect persisted for 2 years after applications ceased. The numerical response of
P. melanarius to dairy slurry required several months, with other carabid species being largely unaffected by the treatments. Species diversity decreased with the number of years of dairy slurry application and with increasing application rates, and the effect persisted for 2 years. The decline in diversity was usually caused by changes in numbers of
P. melanarius. Chemical fertilizer had no effect on carabid populations compared to controls. Earthworm biomass increased with increasing dairy slurry rate. The predatory capacity of the carabids increased with increasing dairy slurry rate, and the proportion of onion maggot pupae,
Delia antiqua, consumed increased with
P. melanarius numbers. The application of dairy slurry may therefore be used to improve pest control in forage grass.
Blueberry scorch virus, a commercially important Carlavirus in highbush blueberry, Vaccinium corymbosum L., is vectored by aphids (Hemiptera: Aphididae). We surveyed the aphids, primary parasitoids ...(Hymenoptera: Aphelinidae, Braconidae), and associated secondary parasitoids (Hymenoptera: Charipidae, Megaspilidae, Pteromalidae) on highbush blueberry and other Vaccinium in the Pacific Northwest from 1995 to 2006, with samples concentrated in 2005 and 2006, to lay the groundwork for augmentative biological control. Ericaphis fimbriata (Richards) was the principal aphid. The dominant parasitoid species were Praon unicum Smith, Aphidius n. sp., A. sp., and Aphidius ervi Haliday. Their frequency in relation to the other primary parasitoids varied significantly with geographical area; P. unicum dominated the frequency distribution in southwestern British Columbia, A. n. sp., west of the Cascades, and A. sp. and A. ervi east of the Cascades. Among the secondary parasitoids, pteromalids dominated, and their frequency in relation to the other secondary parasitoids was lowest in southwestern British Columbia. The parasitization rate for P. unicum and A. n. sp. in southwestern British Columbia increased from May or June to a maximum of 0.080 ± 0.024 and 0.090 ± 0.084 (SD), respectively, in late July or early August. P. unicum emerged in the spring 4 wk before A. n. sp. The parasitization rate for P. unicum was lower in conventional than organic fields. Whereas aphid density increased monotonically, P. unicum had two spring peaks. A simulation model showed that these peaks could reflect discrete generations. Releases of insectary-reared P. unicum at 150 or 450 DD above 5.6 °C, summing from 1 January, may effectively augment the natural spring populations by creating overlapping generations.
Female adults of the aphidopagous gall midge, Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), showed an olfactory response to honeydew excreted by the green peach aphid, Myzus persicae ...(Sulzer) (Hemiptera: Aphididae) under laboratory conditions. The response was only elicited by treatments with honeydew, whereas aphids, aphids with pepper plants or leaves, and pepper plants or leaves were not attractive to the midges. Dose-dependent responses were observed from whole honeydew, honeydew volatiles extracted in pentane, and honeydew volatiles captured on Porapak Q®. When honeydew was eluted with three sequential pentane washes, a positive response was only observed from the midges for the first wash. Female midges laid more eggs on pepper plants infested with higher densities of M. persicae. The olfactory response of midges to honeydew is discussed with respect to prey location.
Stethorus punctillum Weise (Coleoptera: Coccinellidae) is a Palearctic species first found in North America in the 1940s (Putman 1955). Commercial mass-rearing methods were developed in the late ...1990s (Agriculture and Agri-Food Canada, London, Ontario, and Applied Bio-nomics Ltd, Saanich, British Columbia). The beetle is now released in North America to control two-spotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae). Knowledge of the life-history traits of S. punctillum is necessary for effective use of the predator in greenhouses. Putman (1955) provides useful information, but his results cannot be readily interpreted with respect to larval voracity, lower developmental temperature threshold, and developmental time in degreedays (°d), traits that affect efficacy. In this note I report new results relating to these life-history traits and to beetle releases in greenhouse vegetable crops.
Blueberry scorch virus, a commercially important Carlavirus in highbush blueberry, Vaccinium corymbosum L., is vectored by aphids (Hemiptera: Aphididae). We surveyed the aphids, primary parasitoids ...(Hymenoptera: Aphelinidae, Braconidae), and associated secondary parasitoids (Hymenoptera: Charipidae, Megaspilidae, Pteromalidae) on highbush blueberry and other Vaccinium in the Pacific Northwest from 1995 to 2006, with samples concentrated in 2005 and 2006, to lay the groundwork for augmentative biological control. Ericaphis fimbriata (Richards) was the principal aphid. The dominant parasitoid species were Praon unicum Smith, Aphidius n. sp., A. sp., and Aphidius ervi Haliday. Their frequency in relation to the other primary parasitoids varied significantly with geographical area; P. unicum dominated the frequency distribution in southwestern British Columbia, A. n. sp., west of the Cascades, and A. sp. and A. ervi east of the Cascades. Among the secondary parasitoids, pteromalids dominated, and their frequency in relation to the other secondary parasitoids was lowest in southwestern British Columbia. The parasitization rate for P. unicum and A. n. sp. in southwestern British Columbia increased from May or June to a maximum of 0.080 c 0.024 and 0.090 c 0.084 (SD), respectively, in late July or early August. P. unicum emerged in the spring 4 wk before A. n. sp. The parasitization rate for P. unicum was lower in conventional than organic fields. Whereas aphid density increased monotonically, P. unicum had two spring peaks. A simulation model showed that these peaks could reflect discrete generations. Releases of insectary-reared P. unicum at 150 or 450 DD above 5.6 C, summing from 1 January, may effectively augment the natural spring populations by creating overlapping generations.
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